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Reinforced concrete sections have typically been the most used material for hardened protective construction due to their mass and the ductility provided by the reinforcement. The additional mass of these sections reduces deflections and increases dampening, which reduces vibrations. Even for the occasional occurrence of hardened steel structures, the foundation is comprised of reinforced concrete. Reinforced concrete structures are hardened for a multitude of reasons. Some of the most common include antiterrorism, force protection, equivalent protection for quantity distance arc violations, personnel protection, prevention of prompt propagation, asset protection, and elastic response during repeated detonations. Many of the structures used in the Department of Defense (DoD), for these purposes, were built in the United States (US) during the World War II era (1941-1945) for a rapid increase in production and storage of explosives. This puts the average age of many of these facilities at close to 80 years-old, which is past their originally intended service life. This paper presents a structural health and visual inspection technique developed by the U.S. Army Corps of Engineers (USACE) Engineering and Support Center Huntsville (CEHNC) Facilities Explosives Safety Mandatory Center of Expertise (FES MCX) and the Engineering Research and Development Center (ERDC) Geotechnical and Structures Laboratory (GSL) for the inspection of reinforced concrete earth covered magazines (ECMs) [9]. This inspection process has been utilized to inspect over 1500 earth covered magazines across multiple countries over the last decade and aid DoD installations in planning and budgeting for concrete repairs and ECM replacements. The CEHNC FES MCX partners with ERDC for concrete coring and testing of samples to determine the estimated remaining service life of concrete structures based on the carbonation front of cored samples determined by the carbonation tests in relationship to the steel reinforcement. Examples of historical application will be given, and details provided on how these methods can lead to improved life-cycle cost and decision making.

Reinforced concrete sections have typically been the most used material for hardened protective construction due to their mass and the ductility provided by the reinforcement. The additional mass of these sections reduces deflections and increases dampening, which reduces vibrations. Even for the occasional occurrence of hardened steel structures, the foundation is comprised of reinforced concrete. Reinforced concrete structures are hardened for a multitude of reasons. The most common include antiterrorism, force protection, equivalent protection for quantity distance arc violations, personnel protection, prevention of prompt propagation, asset protection, and elastic response during repeated intentional detonations. Many of the structures in the United States (US) used by the Department of Defense (DoD), to accommodate a rapid increase in production and storage of explosives were built during World War II (1941-1945). Facilities used for explosives production, maintenance, research and development (R&D), demolition, testing, and training are commonly referred to as Explosives Operating Locations (EOLs). This puts the average age of many of these facilities close to 80 years-old, which is past their originally intended service life. This paper presents a structural health and visual inspection (SHVI) technique developed by the U.S. Army Corps of Engineers (USACE) Facilities Explosives Safety Mandatory Center of Expertise (FES MCX), the University of Oklahoma, and the Engineering Research and Development Center (ERDC) Geotechnical and Structures Laboratory (GSL) for the inspection of reinforced concrete Explosives Operations Location (EOL) facilities and live-fire training facilities [9]. This inspection process has been utilized to inspect over 1500 structures across multiple countries over the last decade and aid DoD installations in planning and budgeting for necessary repairs and future recapitalization priorities. This work does not include application to anti-terrorism or force protection in hardened structures for conventional weapon effects. This process has also been modified for use in live-fire training operations in concrete facilities and coupled with analyses to determine facility adequacy for explosives operations with desired charge weights, based on the given facility’s current structural health rating and its analyzed ability to remain elastic during repeated intentional detonations. The FES MCX partners with ERDC for concrete coring, materials analysis, and testing of samples to determine the estimated remaining service life of concrete structures based on the carbonation front of cored samples determined by the carbonation tests in relationship to the steel reinforcement. Examples of historical application will be given, and details provided on how these methods can lead to improved life-cycle cost for concrete structures and paired with design development criteria for optimal results.

The presence of chloride ions is one of the most widespread causes of corrosion initiation in reinforcing steel in concrete. Trace chlorides present in cementitious materials or admixtures typically result in very low fresh chloride contents in normal-strength concrete that do not present a danger of corrosion. UHPC mixture designs, however, use much higher dosages of cementitious materials and admixtures that can result in non-negligible total fresh chloride contents. These high chloride values are likely to occur more frequently in the future as more UHPC mixtures are made with locally available materials and alternative cementitious materials and may result in concrete mixtures failing to meet specifications for fresh chloride content limits that are based on mixture proportions used in normal-strength concrete mixtures. UHPC and normal concrete samples were made without fibers and with increasing levels of internally admixed chlorides for four different levels of strength to determine chloride thresholds for internally added chlorides. The chloride threshold for fresh concrete was measured using a slightly modified version of the accelerated test EN 480-14. The water-soluble and acid-soluble chloride ion content of UHPC mixtures tested were measured according to ASTM C1218 and Florida Method FM 5-516 to determine the bound chlorides and fresh chloride limits for corrosion. The results demonstrate that the UHPC had ~ 25% higher chloride threshold than the control mixture when measured as an absolute content per unit volume of concrete. When the UHPC chloride content is normalized by mass of cementitious material, it was found that the amount needed to initiate corrosion may be lower than fresh chloride limits given in ACI-318 and ACI 222. Therefore, the ACI-318 water-soluble chloride limits as a % by mass of cementitious materials were found to be non-conservative for the two of the UHPC mixtures tested and should be re-examined for UHPC.

The addition of supplementary cementitious materials (SCMs) to low-carbon concrete mixtures has been investigated in recent years as part of the sustainability of the concrete sector. Recently, most traditional SCMs, such as fly ash and blast furnace slags, have become unavailable in several developed countries, mostly due to environmental restrictions. Consequently, several new by-products from fast-growing sectors are being considered as potential replacements for traditional SCMs. However, the durability of these new by-products in low-carbon concrete has not been thoroughly explored. As a result, this paper presents the first part of a project related to an extensive experimental characterization, in which low-carbon concrete with high compactness, paste optimization, and partial cement replacement by the addition of waste by-products from the agricultural, metallurgical, paper, and glass industries is studied. Alternative SCMs including rice husk ash, biomass fly ash, rock wool residues, or waste foundry sand are incorporated into corresponding mortar matrices and the results concerning the mechanical properties (flexural and compressive strength) and durability (capillary water absorption, surface electrical resistivity, and carbonation resistance) are presented and analyzed. The outcomes indicate that it is possible to reduce the Portland cement content without compromising the mechanical and durability properties of the concrete.

Even at a level of less than 0.5% by mass of aggregate, pyrrhotite can cause extensive cracking and crumbling of concrete. Because such type of deterioration is rather new, a proper testing protocol to forecast potential damage in concrete is needed. The article discusses important factors that should be considered when developing such performance-based test protocol.